Conventionally, devices in which a circuit assembly provided with a circuit board on which various electronic components are mounted is accommodated in a case are known as devices for energizing and de-energizing in-car electric components.
In such devices, the electronic components mounted on the circuit board generate a relatively large amount of heat, and thus if heat generated by the electronic components stays in the case, the temperature in the case will increase, causing a risk that the performance of the electronic components accommodated in the case will decrease.
Accordingly, various structures for discharging the heat generated by the circuit board or the electronic components have conventionally been proposed. For example, a circuit assembly has been proposed that has a configuration in which a metal heat discharging member is provided on that surface of a circuit board that faces away from the surface on which electronic components are arranged.
The circuit board and the heat discharging member are bonded to each other, by first providing, on one surface side of the heat discharging member, an insulating layer for insulating the heat discharging member from the circuit board, and then spreading an adhesive having high heat conductivity on the insulating layer.
There is a method in which, for example, a thermosetting adhesive is applied to the upper surface of the heat discharging member, and is heated so as to form an insulating thin film that serves as the above-described insulating layer.
However, the method in which a thermosetting adhesive is applied and hardened to form an insulating layer needs a large-scaled device, and incurs a manufacturing cost. Therefore, a method has been considered that uses an adhesive that can be hardened at room temperature, but such an adhesive cannot be used in processes such as printing or spraying since it is hardened at room temperature with time, and it is difficult to form a uniform layer for achieving reliable insulation.
Alternatively, it is also conceivable that an insulating sheet that has adhesion on both sides thereof is used to achieve both insulation and adhesion between the heatsink and the circuit board, but it is difficult to bond the circuit board to the heat discharging member in a uniform state because uniformly applying a constant pressure to the circuit board on which the electronic components are mounted is difficult.
The technique disclosed in the present description was made in view of the above-described circumstances, and it is an object thereof to provide a circuit assembly and an electrical junction box that have a low manufacturing cost, and are superior in heat discharge performance.